1. Field of the Invention
The present invention relates to a method of magnetically transferring magnetic information recorded in a master medium to a slave medium.
2. Description of the Prior Art
The magnetic transfer method is one for magnetically transferring magnetic patterns corresponding to magnetic information (for example, servo signals) recorded in a master medium to a slave medium by applying magnetic field for transferring in a state where the master medium and the slave medium are in close contact with each other. This magnetic transfer method is disclosed, for example, in Japanese Unexamined Patent Publication No. 63(1988)-183623, 10(1998)-40544, 10(1998)-269566 and the like.
However, if foreign matter such as dust exists between the master medium and the slave medium in magnetically transferring the magnetic pattern from the master medium to the slave medium, a space is created between the master medium and the slave medium, and hence areas where no magnetic transfer is performed occur. If the areas where no magnetic transfer is performed occur, the magnetic information is not transferred in these areas, and missing signals in the magnetic information transferred to the slave medium occur. When the recorded signals are servo signals, a satisfactory tracking function cannot be sufficiently obtained, and reliability of reproducing the information signals is lowered.
The foreign matter such as dust mainly adheres to the slave medium. Most of the substances adhering to the slave medium are dust and fiber waste mixed in manufacturing steps of the slave medium.
As described above, the magnetic transferring method is performed in such a manner that the master medium and the slave medium are made to be in close contact with each other, and information signals recorded in the master medium are magnetically transferred to the slave medium by applying a magnetic field to them. In the magnetic transferring step, the substances adhering on the surface of the slave medium move to the master medium, and the quantity of substances adhering to the master medium increases as the number of times of transferring increases, resulting in the occurrence of missing signals.
Furthermore, some of the master mediums have a substrate made of an insulator, and a magnetic layer made of a metal thin film is formed in magnetic patterns corresponding to servo signals in the information bearing plane of the maser medium. The metal thin film electrically floats, or the master medium itself electrically floats. If the metal thin film or the master medium electrically floats, the master medium is made to be a charged state, and dust and the like is apt to adhere to the surface of the master medium. Adhesive power of the adhering substances increases, thus increasing a quantity of movement of the dust from the slave medium to the master medium.
The present invention was made from in view of the above described problems. The object of the present invention is to provide a method of magnetically transferring information signals from a master medium to a slave medium, which is capable of preventing the occurrence of missing signals in magnetically transferring the information signals by reducing a quantity of dust moving and adhering to the master medium, thus achieving a magnetic transfer of the information signals with a high reliability.
The method of the present invention, which allows a master medium and a slave medium to be in close contact with each other, and magnetically transfers information signals recorded in the master medium to the slave medium by applying a magnetic field for transferring to them, comprises the step of electrically grounding a metal thin film formed on a substrate of the master medium.
The metal thin film is directly grounded, or the metal thin film is grounded through the substrate when the substrate is an electrical conductor.
As the foregoing magnetic transfer method, the slave medium is first subjected to DC magnetization in a tracking direction, and the slave medium is allowed to be in close contact with the master medium for use in a magnetic transfer, in which a magnetic layer is formed in micro uneven patterns corresponding to information signals, which are to be transferred. Transfer magnetic field should be applied to the master medium and the slave medium in a direction approximately reverse to an initial DC magnetization direction for the slave medium. A servo signal is preferred as the foregoing information signal.
According to the present invention, the metal thin film formed on the substrate of the master medium is electrically grounded. Accordingly, electric charges of the master medium are discharged, and it is possible to control the dust and the like adhering to the slave medium from moving to the master medium accompanying the close contact of the master medium with the slave medium in magnetically transferring the information signal from the master medium to the slave medium. A quantity of dust adhering to the master medium is reduced even when the magnetic transfer is performed many times. It is possible to prevent the occurrence of missing signals due to insufficient contact of the master medium with the slave medium resulting from the existence of dust adhering to the master medium. The magnetic transfer can be performed with stabile quality, and an enhancement of reliability can be achieved.